Deepest Probe of a Magnet's Workings Could Boost Computers

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In a development that holds potential for both data storage and
biomedical imaging, researchers have used a new technique to
obtain the highest-ever resolution scan of the inside of a
magnet.

The scientists took a tiny magnetic disk – measuring only two
micrometers (millionths of a meter) across and 40 nanometers
(billionths of a meter) thick – and were able to obtain magnetic
resonance image (MRI) scans of its interior.

MRI is the same biomedical scanning technology doctors use to
create detailed 3-D images of the insides of the human body for
medical diagnoses.

Studying the material's behavior at these tiny scales is key to
incorporating it into
computer chips and other electronic devices, scientists say.

Ferromagnets – the type of magnet used in this study – are
magnets made of ferrous metal such as iron. Common household
refrigerator magnets are ferromagnets.

Because ferromagnets retain a particular polarization once
magnetized, they are already essential components in today's
computers and other electronics, where they provide data storage
alongside computer chips. But smaller magnets built directly into
a computer chip could do even more, the researchers explained.

"We know that shrinking these magnets to the nanoscale and
building them directly inside electronics would enable these
devices to do more, and with less power consumption," said Chris
Hammel, lead author of the paper published today in Nature and a
professor of physics at The Ohio State University.

"But a key barrier has always been the difficulty of imaging and
characterizing nanomagnets."

New ways to scan

Typical MRI machines work by inducing a magnetic field inside
non-magnetic objects, such as the human body. Since ferromagnets
are already magnetic, conventional MRI cannot see inside them.

In 2008, Hammel's team debuted a new kind of high-resolution
scanning system that combines three different kinds of
technology: MRI, ferromagnetic resonance, and atomic force
microscopy.

The combination technique that the Ohio State researchers
invented is called "scanned probe ferromagnetic resonance
imaging," or scanned probe FMRI, and it involves detecting a
magnetic signal using a tiny silicon bar with an even tinier
magnetic probe on its tip.

In Nature, they report a successful demonstration of the
technique, as they imaged the inside of the magnetic disk 0.2
micrometer (200 nanometers) at a time. They used a thin film of a
commercially available nickel-iron magnetic alloy called
Permalloy for the disk.

"In essence, we were able to conduct ferromagnetic resonance
measurements on a small fraction of the disk, then move our probe
over a little bit and do magnetic resonance there, and so on,"
explained Denis Pelekhov, director of the ENCOMM NanoSystems
Laboratory at Ohio State. "Using these results, we could see how
the magnetic properties vary inside the disk."

Computers with magnets in their central processing units (CPUs)
would never have to boot up. The entire computer would be
contained inside the CPU, making such devices even smaller and
less power-hungry as well.

Hammel believes that the technique could also one day be useful
tool in biomedical research labs.

Researchers could use it to study tissue samples of the plaques
that form in brain tissues and arteries, and perhaps develop
better ways of detecting them in the body. Knowing how these
plaques form could
advance studies of many diseases, including Alzheimer's and
atherosclerosis.